I noticed that you didn't take in to account all the places where Tweets get republished, often with links without nofollow. I'm not saying that it wasn't all the retweets that gave this result but I am actually saying that we know nothing more from this study than we did before.

A few of the links I found: http://www.google.com/search?hl=en&safe=off&tbo=1&biw=1604&bih=795&tbs=rltm%3A1&q=%22http%3A%2F%2Fbit.ly%2FetMgwU%22+-site%3Atwitter.com&aq=f&aqi=&aql=&oq=